As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for batteries as energy sources, and thus a lot of research has been conducted on batteries capable of satisfying various demands.
Representatively, there is high demand for a prismatic secondary battery and a pouch-type secondary battery which have a small thickness to be applicable to products such as mobile phones in terms of a battery shape, and there is high demand for a lithium secondary battery such as a lithium ion battery and a lithium ion polymer battery with high energy density, a high discharge voltage, and output stability in terms of a material.
However, the lithium secondary battery has a drawback in terms of safety, despite all these merits. Specifically, when the lithium secondary battery reaches an abnormal operation state such as an internal short circuit, an overcharge, exposure to a high temperature, and the like after being finally sealed, a high pressure gas may be generated when an electrolyte therein is decomposed. Herein, the generated high pressure gas may cause deformation of a battery case and shorten a cycle-life of the battery, and more seriously, may cause ignition or explosion of the battery.
Conventionally, in order to improve safety of a lithium secondary battery, a method of using a PTC (positive temperature coefficient), a fuse, a protective circuit under a reduced pressure, or the like, a method of including an additive for improving safety of an electrolyte or an electrode, or the like has been used, but the lithium secondary battery still has a problem of gas generation due to an abnormal reaction inside the battery under an abnormal condition or performance deterioration due to inclusion of the additive, even though the battery is provided with this equipment.
In addition, as a conventional part functioning as a gas pocket tends to gradually disappear along with a recent increase and requirement of higher energy density, a new method for preventing ignition or explosion of a battery during gas generation therein and efficiently removing gas without deteriorating overall performance of the battery is required.